1. Field of the Invention
The present invention relates generally to generators and motors and, more particularly, to regulating their voltage and power by mechanically varying the radial gap between a stator comprised of conductive windings and a rotor that includes a Halbach magnet array.
2. Description of Prior Art
There are numerous applications that require compact pulsed-power systems with power outputs of hundreds of megawatts, associated with energy storage capabilities of hundreds of megajoules. These range from emergency power needs and utility electric power conditioning and stabilization, to pulsed laser fusion or magnetic fusion systems. Utilities employ battery banks or large cryogenic systems including superconducting magnets for energy storage. Condenser banks are commonly used in laser and magnetic fusion applications.
Flywheel energy-storage systems with rotors fabricated from high-strength fiber composite are integrated with high-power electrical generators for use during unexpected intermittent loss of network electrical power to sensitive electronic equipment, such as computers or automated production lines. Flywheel energy storage systems typically operate over a range of angular velocity lying between a maximum determined by structural limitations, and one-half the maximum, at which point ¾ of the kinetic energy of the flywheel has been extracted. In the absence of voltage compensation, the output voltage will fall to half its initial value at this point. However, compensating for this great a change by electronic regulation or external circuits is expensive. An example of a means for regulation of the voltage that requires external circuitry is described in U.S. Pat. No. 5,883,499, “Method for Leveling the Power Output of an Electromechanical Battery as a Function of Speed,” issued to the present inventor.
Halbach arrays comprise the most efficient way to employ permanent-magnet material for the generation of dipole and higher-order pole magnetic fields within a given volume of space. They require neither “back-iron” elements nor iron pole faces in their construction, and they produce fields that approach the theoretical ideal of field uniformity (dipole arrays) or of sinusoidal variation with rotation (higher-order arrays). As such they are ideally suited for use in generators or motors constructed with air-cored stator windings; that is, windings constructed without the use of the laminated iron elements typically used in conventional generators and motors. Using air-cored stator windings avoids the hysteresis losses and limitation on the peak power caused by the magnetic saturation of laminated iron elements and the increased inductance of the stator windings in comparison to air-cored stator windings.
A generator/motor that employs a dipole version of a Halbach array is described in U.S. Pat. No. 5,705,902, titled “Halbach Array DC Motor/Generator,” issued to Bernard T. Merritt, Gary R. Dreifuerst, and Richard F. Post, the present inventor. A generator/motor system that employs higher-order Halbach arrays to produce its magnetic fields is described in U.S. Pat. No. 6,111,332, titled “Combined Passive Bearing Element/Generator Motor,” also issued to Richard F. Post.
The present invention incorporates novel features in such a way as to improve the performance of motor/generators incorporating Halbach arrays, and overcome limitations and drawbacks of the prior art.